Control by Nutrition and Water Stress
Mineral nutrition and water stress are generally believed to be of secondary importance in flower initiation. In many photoperiodic and cold-requiring plants, changes in the supply of N are unable to alter the inductive requirements. Besides its modulating effect on flower initiation in plants grown in environmental conditions that promote flowering, mineral nutrition alters qualitatively the basic inductive requirements in a few species. In the cold-requiring plants, Dactylis glomerata and Geum urbanum, a high nutritional level, together with a high irradiance in the case of Geum, may substitute for vernalization. At an intermediate nutritional level it is a DNP. The literature is rich in preliminary observations suggesting that water stress might be of importance for flower initiation in some plants. Both water stress and chilling reduce growth and result in starch and protein hydrolysis with the consequence of an increased availability in soluble carbohydrates and amino acids, especially praline.